PROJECT SUMMARY Prior research has demonstrated that successful hand recovery in individuals with mild stroke is best achieved through an intervention that is both ?intense? and ?functional?. However, in individuals with moderate to severe post stroke hand paresis, current evidence for an effective intervention to regain hand function is almost absent. A possible contributor to poor recovery in these individuals may be the inability to intensively practice with the paretic hand during activities of daily living (ADLs). Many ADLs require the usage of the hand together with the paretic arm. Due to abnormal muscle synergies following stroke, functional arm movements, such as lifting or reaching, often result in unwanted activity in the wrist/finger flexors. This makes voluntary hand opening more difficult. A possible solution to enable these individuals to practice with their paretic hand in a functional context is using rehabilitation devices to assist hand control. Unfortunately, most of currently available portable hand rehabilitation devices do not sufficiently address hand control with the appearance of abnormal arm synergies. Therefore we propose the development of an individualized, synergy resistant, electromyographic (EMG)-driven functional electrical stimulation (FES) device that allows for Reliable and Intuitive control of the hand (ReIn-Hand) while using the paretic arm during lifting and reaching (aim 1). Furthermore, to enable sufficient practice intensity, we propose to develop the ReIn-Hand device with easy-to- use utilities, like portable and user-friendly, such that it can be employed both in the clinic and at home. To implement this, we propose to develop a user customized forearm/hand orthosis that has 1) EMG recording and stimulation electrodes embedded, and 2) an inertial measurement unit to detect the amount of forearm rotation, which will be used to auto-select the recording/stimulation elements in the electrode-array (aim 2). We will use both a lab-based cross-sessional testing and a home-based longitudinal testing to evaluate the performance of the engineering aspects of this project, including 1) the efficiency of algorithms in the mobile device (aim 1), and 2) the success of FHO design, which is expected to reduce the setup time and allow for its reproducible usage at home (aim 2). Furthermore, we will collect usability feedback from both clinicians and stroke participants to direct further modifications of the ReIn-hand device. By the end of this study, a novel EMG-driven FES prototype will be ready for further testing, both in the clinical and home settings. In the near future, it will act as a research tool to investigate whether long-term intensive and functional use of the paretic hand during functional arm movements will increase the hand function in post-stroke individuals with moderate to severe hand paresis.